1. Field of the Invention
This invention relates to sensing devices and, more particularly, to a system for displaying in two dimensions a map of a physical variable which varies in space.
2. Description of the Prior Art
In scientific investigations it is often desirable to measure a physical variable, such as pressure, temperature, solidity, etc., over an area in space. The usual technique for obtaining a map of the physical variable involves scanning the area to be measured with an appropriate sensor while the position of the sensor is measured. A large number of measurements or samples of the sensor output are then recorded along with the corresponding position information. For example, in wind tunnel tests it is highly desirable to measure pressure in a plane perpendicular to the wind axis adjacent or downstream from the object under test.
Regardless of the nature of the physical variable measured in accordance with the above-described technique, the result of the measurement is a large table of numbers which, in their raw form, are generally meaningless. In order to obtain useful information from the samples, it is necessary to extensively analyze the samples, generally with a digital computer. The computer can then be used to generate a meaningful presentation of the samples. The primary disadvantages of this technique are twofold. First, analysis of the samples requires relatively expensive data processing equipment to analyze the samples using elaborate interpolation procedures. Second, the extensive nature of the computer analysis requires a great deal of time so that there is a substantial delay in obtaining the map after the measurements have been completed.
An additional problem with the above-described technique results from the difficulty in obtaining accurate position measurements. The sensor is generally mounted at the end of an elongated sensing probe, and the position of the sensor is measured by measuring the movement of the probe at a substantial distance from the sensor. The sensor is often subjected to substantial forces transverse to the longitudinal axis of the probe, causing the probe to bend significantly. As a result, the measured position of the sensor does not correspond to the actual position of the sensor. These measurement errors can be quite detrimental to achieving a high spatial resolution in the map.
In another context, light-emitting devices have heretofore been used in various systems to measure the position of objects. For example, U.S. Pat. No. 1,568,544, issued to Chilton et al., discloses a torsion-sensing device mounted on a crankshaft. The device includes a light, the radial position of which is proportional to the torsion of the crankshaft. The path of the light as the crankshaft rotates is examined to provide an indication of the crankshaft torsion through the full 360 degrees of rotation. It should be understood that the illumination from the lamp is constant, the magnitude of the torque being indicated by the radial position of the lamp and not its intensity.
U.S. Pat. No. Re. 28,661, issued to Tredway, Sr., discloses a lamp mounted on a golf glove for displaying a pattern on a wall in front of the golfer as the golfer swings. The characteristics of the pattern identify various chracteristics of the golfer's swing.
U.S. Pat. No. 2,813,421, issued to Cheney et al., discloses a system for plotting the pressure along the length of the wind tunnel. In the Cheney et al. device, a pressure-sensing probe is mounted on a carriage which moves along the wind tunnel. The output of the sensor drives one axis of the plotter, while a transducer measuring the position of the sensor drives the other axis of the plotter. The Cheney et al. device does not utilize any light-emitting device.
U.S. Pat. No. 3,197,675, issued to Fruengel et al., discloses a system for performing high-speed photography of gas flow phenomena. Basically, this system utilizes a spark gap to generate a plasma which is carried in a stream of flowing gas. The plasma is photographed as it flows around objects in a gas stream in order to record the flow characteristics.